The present invention relates to a developing device having a detachable developer cartridge, an image forming unit (i.e., a process cartridge) and an image forming apparatus.
An image forming apparatus using electrophotography is generally configured to form a latent image on a surface of a photosensitive drum, develop the latent image using a developing device to form a toner image, and transfer the toner image to a recording medium. The developing device has a main body, and a detachable toner cartridge storing a toner (i.e., a developer). The main body has a toner receiving opening (i.e., a developer receiving opening) for receiving the toner supplied by the toner cartridge. Such a developing device is disclosed in, for example, Japanese Laid-open Patent Publication No. 2008-20605 (see, paragraphs 0018 and 0022).
In a general developing device, when the toner cartridge is detached from the main body of the developing device for replacement, the toner receiving opening is left open, and therefore foreign matters may enter the toner receiving opening.